1. Field of the Invention
The present invention relates to an information reproducing apparatus, and more particularly to such an apparatus for reading the same information plural times and selecting one of the plural readings for information reproduction, adapted for use, for example, in an optical information reproducing apparatus.
2. Related Background Art
Reproduction of information utilizing an optical information recording medium such as a compact disk or an optical file has become popular in recent years. Also, more recently, there has been investigated reproduction of information utilizing a cardshaped optical information recording medium (hereinafter called an optical card) of superior portability compared with the above-mentioned recording media and having a relatively large memory capacity.
FIG. 1 is a schematic plan view showing an example of the recording format on such an optical card.
As shown in FIG. 1, the optical card 1 is provided thereon with a recording area 2, consisting of an array of plural bands 3. Each band 3 consists of an array of plural information tracks 4, each having a storage capacity of several tens to a hundred bits. The bands are separated mutually by reference lines 5. An arrow A shows the moving direction of the optical card 1 in the reproduction of information, and an arrow C indicates the scanning direction of an optical head for information reading at the reproduction of information.
FIG. 2 is a partial magnified schematic view of the above-explained recording format of the optical card, showing an end of the optical card 1 in the direction A.
In FIG. 2, a hatched area indicates information "1", while a blank area indicates information "0". In an information track area 201, a linear array of information bits in the direction C constitutes an information track. A band 3 is composed of reference lines 5 and an information track area 201. The band 3 extends in the up and down directions in FIG. 2.
FIG. 3 is a schematic view of an apparatus for reproducing information from an optical card having the above-mentioned recording format, and FIG. 4 is a partial perspective view thereof.
In FIGS. 3 and 4, the optical card 1 can be reciprocated in the direction A by a rotary mechanism 6. The information recorded on the optical card 1 is read and reproduced, track by track, by an optical head 11. At first the light from a light source 7 such as a light-emitting diode is focused by a lens system 8 and illuminates the optical card 1. Thus, the image of a track on said optical card is focused, by an imaging optical system 9, on a linear CCD sensor array 10. Since the optical card 1 moves in the direction A, the image of the information tracks correspondingly moves on the sensor array 10. The sensor array 10 scans the image several times while each information track is focued on the sensor array 10. In this manner, the information recorded in information tracks of a certain band is reproduced, and then the optical head 11 is suitably moved in a direction C for focusing an information track of another desired band on the sensor array, thereby reproducing the recorded information in the same manner as described before.
The data recorded on the optical card 1 are generally encoded by 4/5 conversion, MFM modulation, etc. In the 4/5 conversion, the data after conversion show bit inversion intervals of 1T, 2T and 3T only (wherein T is the minimum interval of bit inversion by modulation). Also, in the MFM modulation, the data after modulation show bit inversion intervals of 1T, 1.5T and 2T only. Consequently, the reference line can be easily distinguished from the information track by forming, in the reference line 5, a bit pattern of a larger inversion interval than the maximum bit inversion internal appearing in the information track 4. For this purpose a pattern with a bit inversion interval of 4T in the case of 4/5 conversion, or of 3T in the case of MFM modulation can be formed in the reference line.
Also, the neighboring tracks can be distinguished by alternately inverting the patterns of the reference lines 5 of the tracks neighboring in the direction A as shown in FIG. 2.
FIG. 5 is a block diagram of a reproducing apparatus used for reproducing the information recorded on the above-described optical card.
In FIG. 5, a sensor array 10 is driven by a drive clock signal 307 from a sensor array driver 306, and the output signal of the sensor array is amplified in the driver 306 and is supplied as a video signal 309 to a binary digitizing circuit 310. An NRZI signal 311 obtained in the circuit 310 is supplied to a clock reproducing circuit 312, a demodulator circuit 314 and a reference line detecting circuit 316.
The clock reproducing circuit 312 extracts a clock signal 313 from the NRZI signal 311 and supplies it to the demodulator circuit 314, which generates a demodulated NRZ signal 315 in response to the clock signal 313 and the NRZI signal 311.
On the other hand, the reference line detecting circuit 316 receives a clock signal 318 obtained by dividing the drive clock signal 307 in a frequency divider circuit 317 and the NRZI signal from the binary digitizing circuit 310, and supplies the demodulator circuit 319 with a reference line detection signal 319.
The demodulating operation of the demodulator circuit 314 is turned on and off according to the reference line detection signal 319, so that the data read between two reference line detection signals are released as an output signal 315.
In the above-explained reproduction of the information recorded on an optical card, since the scanning operation of the sensor array 10 is not synchronized with the relative movement of the optical card 1 with respect to the sensor array, the reproduced information is obtained usually by reading the same information track plural times and selecting the information of one of such plural readings. Such selection of information can be achieved, for example, by selecting the first information obtained in a proper manner.
However, errors may be generated by various causes in the process of reproducing information from the optical card 1, so that the signals reproduced from the same information track are not necessarily same.
Consequently, in an information reproducing apparatus, it is desirable to provide the information of highest accuracy among those obtained in plural readings.